1. Field of the Invention
The present invention generally relates to integrated circuits, and more particularly to copper interconnect structures.
2. Background of Invention
In damascene processing or dual-damascene processing, an interconnect structure or wiring pattern can be formed within a dielectric layer. Using known techniques a photoresist material may be used to define the wiring pattern. The patterned photoresist acts as a mask through which a pattern of the dielectric material can be removed by a subtractive etch process such as plasma etching or reactive ion etching. The etched openings may be used to define wiring patterns in the dielectric layer. The wiring patterns may then be filled with a metal using a filling technique such as electroplating, electroless plating, chemical vapor deposition, physical vapor deposition or a combination thereof. Excess metal can then be removed by a chemical mechanical polishing process.
In a single damascene process, via openings may be provided in the dielectric layer and filled with a conducting metal, which may often be referred to as metallization, to provide electrical contact between layers of wiring levels. In a dual damascene process, the via openings and the wiring pattern are both provided in the dielectric layer before filling with the conducting metal. Damascene processing followed by metallization may be used for each layer until the integrated circuit device is completed.
Barrier layer films may be needed between the dielectric material and the conductive material in order to prevent atoms of the conductive material from migrating into and at times through the dielectric material and into other active circuit device structures. For example, barrier layers can be used in conjunction with conductive materials, such as those used in interconnect wiring layers, to isolate the conductive materials from the dielectric material. Migration of conductive material in the device can cause inter-level or intra-level shorts through the dielectric material. In some cases, device functionality can be destroyed. Due to device scaling, barrier layers may have thinner dimensions because of the smaller dimensions of the interconnect structures.
Migration is a particular concern when copper is used as the conductive interconnect material because copper exhibits relatively high mobility in dielectric materials used in semiconductor wire structures. Yet, in spite of this problem, copper is a favored material for interconnects because of its superior conductivity and good electromigration resistance. As a result, if copper is used in an interconnect structure, the copper may need to be confined by a barrier layer.
A barrier layer conventionally used in conjunction with copper interconnect structures may be tantalum and tantalum nitride. Alternatively, titanium and titanium nitride have been used as a barrier layer to prevent the migration of copper into the dielectric material, as well as a titanium or titanium oxide barrier layer. However, because these barrier materials are more reactive than copper, the formation of interfacial oxides can result in poor adhesion properties between the deposited copper and the barrier material. Due to the presence of the contaminating oxides, these conventional barrier materials usually require the deposition of a copper seed layer prior to standard copper electrodeposition in a copper acid bath. Electrodeposition of copper is generally only suitable for applying copper to an electrically conductive layer. As such, the copper seed layer provides the additional purpose of being electrically conductive to facilitate the electrodeposition of copper.
The copper seed layer may contain other materials such as manganese to add alloy-related enhancements to the Cu interconnect electromigration reliability. After copper is electrolytically deposited on top of a copper-manganese seed layer, the manganese atoms tend to migrate to a top surface of the electrically deposited copper. Migration of the manganese atoms improves electromigration reliability by providing a self-capping effect, which reduces Cu atom diffusivity along the Cu/cap interface. However, when a very thin tantalum nitride barrier layer is first deposited before the copper-manganese seed layer, some oxygen atoms from the dielectric material may breach the barrier layer and intrude into the electrically deposited copper. The oxygen may trap manganese atoms from the copper-manganese see layer, and prevent them from migrating to the top of the electrically deposited copper thereby reducing electromigration reliability.